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What are protistas? Prostista is a kingdom to which the eukaryotic microorganisms, protists belong. Protista was first observed by John Hogg in 1860s as primitive unicellular forms of both plants and animal. At that time, this kingdom was known as 'Protoctista', which literally means first established beings. Later in the year 1866, the term protista was coined by Ernst Haeckel. This kingdom belongs to the domain Eykarya. Recent classifications are being made by scientists where listing of organisms is done on hierarchical basis. They have different characteristics that distinguish them from other kingdoms. The most common examples protista include, amoeba, plasmodium, pararamecium, slime mold, red, brown and golden algae, fungi, diatoms, etc.

General Characteristics of Protista
  • They are mostly unicellular but some are multicellular and colonial organisms.
  • They are either free-living or parasitic.
  • They have aerobic mode of respiration and have mitochondria for cellular respiration.
  • They are true eukaryotes and are nucleated.
  • They have (9+2) arrangement of flagella and have membranous organelles.
  • They reproduce both sexually (syngamy) and asexually.
  • They are grouped into 3 categories: animal like (protozoa), fungus like, and plant-like.
  • According to the categories, they have different modes of nutrition, like heterotrophy or autotropohy.
  • Plant-like protists (algae) have chlorophyll and accessory pigments, named xanthophylls, phycobilins, and carotene.
Classification of Protists - Based on Sub Groups

Plant Like Characteristics: e.g. Algae

They are further classified as Euglenoids, Diatoms, and Dinoflagellates.

Euglenoids Characteristics - e.g. Euglena
  • They are unicellular
  • Animal like movement
  • Flagellum present
  • Presence of nucleus, chloroplasts, flagellum, and cell membrane
  • Asexual reproduction
Diatoms Characteristics - e.g. Chrysophyta (golden algae)
  • Two part shell of silicon glass
  • Golden brown in color
  • Stores food in form of oil
Dinoflagellates Characteristics - e.g. Pyrophyta (red algae)
  • They are di-flagellated
  • Phosphorescent algae
  • Covered with plates
  • Color renders 'red tides'
  • Has toxins
Animal Like Characteristics: e.g. Protozoans
  • Presence of pseudopodia
  • Shell composed of calcium
  • They are heterotrophs
  • Free living, saprophytic, mutualistic or parasitic
The animal-like protistas are further classified as the following:
  • Sarcodina: amoeba like movement (pseudopodia)
  • Flagellates: moves with flagella
  • Paramecium: moves with cilia
  • Sporozoans: produce spores
Fungus-Like Characteristics: e.g. Slime Molds
  • They are multicellular
  • Change forms during life cycle
  • Tend to live in damp climate
  • Plasmodial (acellular), slime molds (Myxomycetes)
Phylogeny of Protista
  • Kingdoms: Chromista, Archaezoa, Protista/Protozoa
  • Candidate Kingdoms: Archaezoa, Euglenozoa, Alveolata, Stramenopila, Rhodophyta
Uses of Protista Cell Wall

The cell wall of red algae is made up of agar and carageenan. Both are used as additives in food. Agar is used as a gelling agent and thickener. Shells made up of calcium carbonate, protects them from grazing animals. In brown algae, cell wall of algin and cellulose protects them against waves and exposure to air. This component ensures uniform freezing and melting of food items. Fungi have cell wall made up of cellulose or chitin.

I hope the information provided about protists has proven useful to you. You can view their images and check out different forms over the Internet to expand your knowledge a little more.